282 OUR INSECT FRIENDS AND FOES 



with a long free flagellum, thought to be a male. 

 In forty-eight hours, trypanosomes of a very 

 different type, with short free flagellae, appear, 

 and in ninety-six hours all traces of the trypano- 

 somes disappears from the tissues of the fly. 

 Although at present unknown, it is quite within 

 the bounds of possibility that the development 

 of the parasite continues in the tissues of the fly 

 in some hitherto unobserved form, causing the 

 insect to again become infective. A curious and 

 interesting fact worth keeping in mind is that a 

 certain percentage of Tsetse-flies, which have 

 never fed upon human or other blood, contain 

 slender and stout forms of trypanosomes in 

 the gut. 



The first printed record of sleeping sickness 

 appears to have been written by Winterbottom 

 in 1803. Writing of Sierra Leone, he states that 

 "the Africans are very subject to a species of 

 lethargy which they are much afraid of, as it 

 proves fatal in every instance." It was also 

 described by early nineteenth-century writers 

 as occurring amongst the imported slaves work- 

 ing on the plantations in Brazil and the West 

 Indies, and it is fortunate for those countries 

 that there was apparently no Tsetse-fly to spread 

 the disease, or probably the greater part of the 

 population would have been wiped out. The 

 disease is caused by the presence and multipli- 

 cation in the blood of a motile, flagellate parasite 

 called a trypanosome, the particular species 

 being called Trypanosoma gambiense. These 

 trypanosomes are not confined to man, but 

 certain species are the cause of various diseases 



